This invention relates generally to fuel delivery systems used with internal combustion engines and, more particularly, to fuel pressure regulation systems designed for marine engines.
Electric motor fuel pumps have been used in a wide range of applications to deliver fuel to internal combustion engines. One such use of electric fuel pumps is in the form of a constant delivery fuel pump, in which the electric fuel pump is operated at a constant speed with a pressure regulator being used to return excess fuel from the engine to the fuel tank. It should be noted that there are many disadvantages associated with a fuel pressure regulator system of this kind. For instance, the returned or excess fuel carries engine heat with it back to the fuel tank, thereby increasing the temperature and vapor pressure within the tank. Venting this vapor pressure into the atmosphere causes pollution problems and adversely affects fuel mileage. Additionally, operating the electric motor at a constant high speed increases energy consumption and reduces the operational life of the fuel pump, fuel filter, and other components of the system.
Another type of fuel delivery application uses a feedback loop to control the speed of the fuel pump, the duration of operation, or other operational parameters of the pump that affect the fuel line pressure. Unlike the constant delivery fuel pump previously described, fuel pressure regulation systems incorporating a feedback loop drive the fuel pump according to required output. For example, see U.S. Pat. No. 4,789,308, which discloses a self-contained fuel pump that includes an electronic sensor at the pump outlet which measures the outlet fuel pressure and modulates the electrical current supplied to the pump motor so as to maintain constant pressure in the fuel delivery line. While it is recognized that fuel pressure regulation systems utilizing pressure sensors and feedback loops avoid many of the drawbacks attributed to constant delivery pumps, such as energy consumption and wear-and-tear, those systems introduce disadvantages of their own. For example, a significant concern confronting the implementation of these pressure sensors is the harshness of the environment in which they are used and, in particular, their incompatibility with the corrosive fuel. Some of these concerns have been mitigated through the use of stainless steel components. However, there remain certain sensor components, such as those located on the reference side of the pressure sensor, which are not protected from the harsh environment, consequently, xe2x80x9coutside-of-environmentxe2x80x9d sensing is often necessary. Also, the measures taken to counter the corrosive conditions of the environment significantly increase the cost of these components.
Thus, it would be advantageous to provide a fuel pressure regulation system having the advantages of closed loop control while avoiding the problems inherent in the use of pressure sensors.
In accordance with the present invention, there is provided a fuel pressure regulation system that uses a control circuit to operate a fuel pump or other fuel pressure control device in one of two or more modes depending upon the input received from a pressure switch in the fuel line. The pressure switch provides the control circuit with an indication of whether the fuel pressure is above or below a reference pressure. When the fuel pressure is below the reference pressure, the control circuit operates the fuel pressure control device in a first one of the modes to increase the fuel pressure towards the reference pressure. When the fuel pressure is above the reference pressure, the control circuit operates the fuel pressure control device in a second one of the modes to provide closed loop control of the operating current supplied to the control device.
Thus, the present invention uses a pressure switch, a current sensor, and a control circuit to provide closed loop control to a fuel pressure control device based on the premise of determining the amount of electric current needed to maintain the fuel pressure at the reference pressure and then regulating the operating current of the fuel pressure control device to maintain that level of current.
Preferably, the control circuit provides a pulse width modulated control signal that is used to operate the fuel pressure control device. Also, the closed loop control is preferably implemented by storing the current signal from the current sensor as a reference value each time the pressure switch detects that the fuel pressure has crossed the reference pressure in the positive (pressure rising) direction, and then using that reference value as a setpoint for the closed loop control.
In accordance with another aspect of the present invention, the fuel pressure regulation system can be implemented as a part of a fuel delivery system for an internal combustion engine. In addition to the components of the fuel pressure regulation system identified above, the fuel delivery system also includes a fuel supply, a fuel delivery pump, and an injector. The delivery pump draws fuel from the fuel supply and delivers it to the fuel pressure regulation system where the system manages the outlet fuel pressure as indicated above. The fuel is then delivered to the injector for subsequent injection into a combustion chamber of the engine.
A primary advantage of this invention is that it permits fuel pressure regulation in a fuel system that can be constructed using an inexpensive pressure switch, with the fuel system obviating temperature drift instability and fuel incompatibility and being more reliable and economical to manufacture and assemble relative to other designs that provide such fuel pressure regulation.